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Mechanical shutdown of battery separators: Silicon anode failure
Get PDFThe pulverization of silicon (Si) anode materials is recognized as a major cause of their poor cycling performance, yet a mechanistic understanding of this degradation from a full cell perspective remains elusive. Here, we identify an overlooked contributor to Si anode failure: mechanical shutdown of separators. Through mechano-structural characterization of Si full cells, combined with digital-twin simulation, we demonstrate that the volume expansion of Si exerts localized compressive stress on commercial polyethylene separators, leading to pore collapse. This structural disruption impairs ion transport across the separator, exacerbating redox nonuniformity and Si pulverization. Compression simulation reveals that a Young’s modulus greater than 1 GPa is required for separators to withstand the volume expansion of Si. To fulfill this requirement, we design a high modulus separator, enabling a high-areal-capacity pouch-type Si full cell to retain 88% capacity after 400 cycles at a fast charge rate of 4.5 mA cm−2. © The Author(s) 2024.TRUEsciescopu
Enhancing Stretchability of PEDOT:PSS Films with Ionic Liquid Pretreatment: A Molecular Dynamics Study
No full textPoly(3,4-ethylenedioxythiophene):poly(stryrenesulfonate) (PEDOT:PSS) is the most promising material for stretchable electronic components because it is stable, transparent and solution processable. However, the pristine PEDOT:PSS thin film has limited electrical conductivity (<10 S/cm) and low yield strain (<6%). The electrical conductivity and stretchability of pristine PEDOT:PSS films can be improved by ionic liquid (IL). We investigate the effect of ILs on the PEDOT:PSS morphology through molecular dynamics simulations of the mechanical properties of PEDOT:PSS subjected to uniaxial strain. Through this, we observe at the molecular level how the morphology change by the IL can improve the stretchability of the PEDOT:PSS. Finally, the principle of improving the electrical and mechanical properties of PEDOT:PSS of the IL is identified, and the design principle of the IL is proposed to control the desired properties
Active Sites of Mixed-Metal Core-Shell Oxygen Evolution Reaction Catalysts: FeO4 Sites on Ni Cores or NiN4 Sites in C Shells?
Get PDFWater electrolysis for clean hydrogen production requires high-activity, high-stability, and low-cost catalysts for its particularly sluggish half-reaction, the oxygen evolution reaction (OER). Currently, the most promising of such catalysts working in alkaline conditions is a core-shell nanostructure, NiFe@NC, whose Fe-doped Ni (NiFe) nanoparticles are encapsulated and interconnected by N-doped graphitic carbon (NC) layers, but the exact OER mechanism of these catalysts is still unclear, and even the location of the OER active site, either on the core side or on the shell side, is still debated. Therefore, we herein derive a plausible active-site model for each side based on various experimental evidence and density functional theory calculations and then build OER free-energy diagrams on both sides to determine the active-site location. The core-side model is an FeO4-type (rather than NiO4-type) active site where an Fe atom sits on Ni oxide layers grown on top of the core surface during catalyst activation, whose facile dissolution provides an explanation for the activity loss of such catalysts directly exposed to the electrolyte. The shell-side model is a NiN4-type (rather than FeN4-type) active site where a Ni atom is intercalated into the porphyrin-like N4C site of the NC shell during catalyst synthesis. Their OER free-energy diagrams indicate that both sites require similar amounts of overpotentials, despite a complete shift in their potential-determining steps, i.e., the final O2 evolution from the oxophilic Fe on the core and the initial OH adsorption to the hydrophobic shell. We conclude that the major active sites are located on the core, but the NC shell not only protects the vulnerable FeO4 active sites on the core from the electrolyte but also provides independent active sites, owing to the N doping. © 2024 The Authors. Published by American Chemical Society.TRUEsciescopu
Gut Microbiota Defines Functional Direction of Colonic Regulatory T Cells with Unique TCR Repertoires
No full textIntestinal microbiota and selected strains of commensal bacteria influence regulatory T (Treg) cell functionality in the colon. Nevertheless, whether and how microbiota changes the transcriptome profile and TCR specificities of colonic Tregs remain to be precisely defined. In this study, we have employed single-cell RNA sequencing and comparatively analyzed colonic Tregs from specific pathogen-free and germ-free (GF) mice. We found that microbiota shifts the activation trajectory of colonic Tregs toward a distinct phenotypic subset enriched in specific pathogen-free but not in GF mice. Moreover, microbiota induced the expansion of specific Treg clonotypes with shared transcriptional specificities. The microbiota-induced subset of colonic Tregs, identified as PD-12 CXCR3+ Tregs, displayed enhanced suppressive capabilities compared with colonic Tregs derived from GF mice, enhanced production of IL-10, and were the primary regulators of enteric inflammation in dextran sodium sulfate-induced colitis. These findings identify a hitherto unknown gut microbiota and immune cell interaction module that could contribute to the development of a therapeutic modality for intestinal inflammatory diseases. © 2024 by The American Association of Immunologists, Inc.FALSEsciescopu
Dynamic Network Slicing Framework in 5G Open-RAN Architecture
No full text5G 오픈랜의 핵심 기술 중 하나인 네트워크 슬라이싱은 네트워크 가상화 기술을 활용하여 단일 물리적 네트워크 인프라를 여러 가상 네트워크로 분할하는 기술이다. 네트워크 자원을 미리 정해진 방식에 따라 고정적으로 분할하여 셀 간 잠재적인 간섭관계의 변화나 채널 환경의 변동성을 유연하게 고려하지 못하는 기존의 개발된 정적 네트워크 슬라이싱 기술과 달리, 사용자의 이동성과 채널 환경에 따라 실시간으로 자원의 할당을 결정하는 동적 네트워크 슬라이싱 기술은 네트워크 성능의 향상과 효과적인 서비스 품질 제어를 가능하게 할 것으로 기대된다. 하지만 동적 네트워크 슬라이싱 기술에서 실시간으로 사용자와 빔 스케줄링, 전송 전력 및 대역폭 할당을 동시에 결정하는 데 발생하는 높은 계산 복잡도로 인해 이들을 최적으로 결정하는 알고리즘의 개발은 불가능하다. 따라서 본 논문에서는 효율적으로 자원 할당을 결정할 수 있는 저 복잡도 동적 네트워크 슬라이싱 알고리즘의 성능을 효과적으로 향상시킬 수 있는 동적 네트워크 슬라이싱 프레임워크를 제안한다
Distinct charge density wave instabilities in PrTen (n=2, 3) and ErTe3 investigated via ARPES and XAS
No full textUnderstanding the origin of distinct charge density wave (CDW) instabilities in layered RTen (n=2, 3) compounds (R, rare earth element) has been an important issue. In this research update, we have investigated the electronic structures of PrTen (n=2, 3) and ErTe3 layered CDW compounds employing angle-resolved photoemission spectroscopy (ARPES) and soft x-ray absorption spectroscopy (XAS). The trivalent valency of R3+ ions is confirmed for PrTen (n=2, 3) and ErTe3, supporting that R-Te slabs serve as charge reservoirs and that the CDW instability occurs in the partially filled Te sheets. Both R4d→4f resonant photoemission spectroscopy and photon-energy map measurements provide evidence that R4f electrons do not contribute directly to the CDW formation but that the indirect contribution from Pr 4f electrons through the Pr 4f-Te 5p hybridization is feasible in PrTen (n=2, 3). Circular and linear dichroism ARPES measurements indicate that the chirality of the Te 5p orbitals certainly plays a role in the CDW formation of RTe3 (R=Pr, Er) while it is relatively weak in PrTe2, and that the EF-crossing orbitals, responsible for the CDW formation, are ordered in plane (in the ac plane) in all of them. Different CDW-induced Fermi surface reconstructions between RTe3 and RTe2 are due to (i) the existence of two Te sheets and one Te sheet per unit cell in RTe3 and RTe2, respectively, so as to produce different numbers of hole carriers, and (ii) the different lattice parameters of Te sheets in RTen, leading to the different densities of states at EF. © 2024 American Physical Society.FALSEsciescopu
리튬이차전지용 AgNO3 담지형 박막 리튬 금속 분말 전극
No full textLi metal powder, Silver nitrate, Nucleation, Lithium nitride, Li metal battery리튬 금속 분말(Li metal powder, LMP)은 슬러리 기반 코팅이 가능하므로 리튬 금속 배터리(Li metal batteries, LMBs)용 대면적 박막 리튬 전극 제작에 유리하다. 또한, 구형의 LMP를 기반으로 제작된 전극은 넓은 반응면적을 가지므로 국부 전류 밀도를 감소시킬 수 있다. 그러나 충전 시 리튬 표면에서의 불균일한 리튬 핵생성 및 성장은 여전히 LMBs의 성능 및 안전성 확보의 걸림돌로 남아 있다.
이에, 본 논문은 LMP 전극 내에 AgNO3를 도입함으로써 리튬의 균일한 전착을 유도하고 높은 이온전도도를 가지는 solid electrolyte interphase (SEI)를 형성하였으며, 결과적으로 장기 수명특성과 고속충전 안정성을 확보하였다. LMP 슬러리 내에 도입한 AgNO3는 리튬과 화학적으로 반응하여 리튬친화도가 높은 금속 Ag를 형성할 수 있으며, LMP 전극 전반에 걸쳐 핵생성 사이트로 작용하여 리튬의 균일한 전착을 유도함을 실험적으로 분석했을 뿐 아니라 밀도범함수이론(density functional theory, DFT) 계산을 통해 금속 Ag가 리튬이온의 전착을 유도함을 확인하였다. 또한, 동일 화학반응을 통해 형성되는 LiNO3는 높은 이온전도도를 가지는 SEI를 형성함으로써 리튬이온 이동 저항을 감소시킬 수 있다. AgNO3가 도입된 40 마이크로미터 두께의 LMP 전극을 적용한 경우, 1C/3C 충전/방전 조건에서 500 사이클 이후에도 86.8 % 용량 유지율을 확보하였으며, 최대 30C 조건에서의 전기화학적 안정성 또한 확인하였다.
핵심어: 리튬 금속 분말, 질산은, 핵생성 사이트, 질산리튬, 리튬 금속 전지
|Li metal powders (LMPs) are beneficial to fabricating thin and large-area Li electrodes for Li metal batteries (LMBs) owing to slurry coating-based manufacturing and facile impregnation of functional additives. 3D structure of LMP-based composites can alleviate the local current density even at a higher current. However, non-uniform nucleation and growth persist as barriers to guaranteeing both the performance and safety of LMBs. Here, we report an AgNO3-preplanted LMP electrode for securing long stable cycling of LMBs. During pre-mixing the LMP slurry with AgNO3 additive, it can chemically form lithiophilic Ag that can offer favorable nucleation sites throughout the LMP surface. At the same time, nitrates can help enrich a highly conductive, robust Li3N into solid electrolyte interphase (SEI). Pre-planting AgNO3 into a 40 μm-thick LMP electrode reinforced the cycling stability up to 500 cycles with 86.8 % capacity retention at 1C/3C charging/discharging rates and allowed superior rate capability up to 30C.
Keywords: Li metal powder, Silver nitrate, Nucleation, Lithium nitride, Li metal batteryⅠ. Introduction 1
1.1 Overview 1
Ⅱ. Materials and Methods 5
2.1 Electrode fabrication 5
2.2 Cell assembly 6
2.3 Electrochemical analysis 6
2.4 Morphological and compositional analysis 7
2.5 Computational method 8
Ⅲ. Results and Discussion 10
3.1 Advantages, structural, and surface analysis of AgNO3-LMP electrodes 10
3.2 Li/Li symmetric cell cycling and surface morphology analysis 14
3.3 Li/Cu cell Coulombic efficiency comparison 16
3.4 Li/NMC622 cell cycling performance 18
3.5 XPS analysis of AgNO3-LMP electrodes 26
3.6 Li/NMC622 cell characterization and high-rate performance analysis 27
Ⅳ. Conclusion 30
References 31
Summary in Korean 36MasterdCollectio
Development of a Throwbot with Shock Absorption Structure
No full textIn this study, a throwing robot equipped with an shock absorbing structure, utilizing paired-Cross Flexural Hinge (p-CFH) and an airbag, was fabricated and validated to assess the effectiveness of its impact absorption mechanism. This robot was developed in anticipation of situations where direct human intervention for life rescue would be challenging. Throwing robots can be broadly categorized into ball type, wheel type, and hybrid type. The hybrid type combines the advantages of both: the ease of throwing from ball type, due to its low air resistance coefficient, and the versatile mobility of the wheel type in diverse environments. However, hybrid type throwing robots are more vulnerable to external impacts due to the complexity of their internal structure, resulting in a lower maximum drop height compared to wheel type robots.To address these challenges, this research proposes a the Throwbot that combines the easy throwing capability of ball type with the obstacle overcoming ability of the wheel type, while also addressing the low free fall height drawback inherent in hybrid types. To achieve this, we developed a Throwbot with a ball to wheel transform structure, p-CFH mechanism, and airbag based impact absorption system. Additionally, materials were selected based on simulation results to refine the Throw-bot. The performance of the proposed robot was evaluated through various assessments, including free fall experiments and obstacle overcoming tests. Through this research, the proposed Throwbot effectively addresses the shortcomings of existing throwing robots, establishing a novel approach to throwing robot design. © 2024 IEEE
Edge-Server Workload Characterization in Vehicular Computation Offloading: Semantics and Empirical Analysis
Get PDFEdge server-assisted computation offloading enables vehicles to leverage server compute resources to deliver connected services, overcoming the limitations of onboard resources. Understanding the compute workloads of edge servers is crucial for effective resource management and scheduling, yet this task is challenging due to the complex interplay of factors such as vehicle mobility and computation offloading patterns. To address this, we propose an empirical analysis framework that systematically characterizes the compute workloads of edge servers. We begin by formalizing the relationships among three key aspects: local load (generated by vehicles), composite load (imposed on edge servers), and traffic flow (vehicle mobility patterns). Our framework then uses models of the local load and traffic flow as inputs to generate the composite loads on edge servers. Experiments were conducted by injecting between 600 and 5,000 vehicles per hour in two distinct geographical areas, New York City and Tampa. We provide a quantitative analysis demonstrating how the composite loads on edge servers vary with changes in traffic flows, geographical areas, and offloading patterns. AuthorsTRUEsciescopu
Satellite System Design for Communication Security and Network Control
No full textMultibeam Satellites;cryptography;physical layer security;transmission;handover1 Introduction 1
1.1 Non-Terrestrial Network 1
1.2 Motivation 2
1.3 Contributions 3
1.4 Outline . 5
2 Cross Layer Encryption of CFB-AES-TURBO for Advanced Data Transmission Security 6
2.1 Introduction . 6
2.2 Related Work 12
2.3 Proposed Joint Security Method 14
2.3.1 Encryption and Encoding . 14
2.3.2 Decoding and Decryption . 16
2.3.3 Encryption Block Size Selection . 18
2.3.4 Key Exchange 20
2.4 Performance Analysis 23
2.4.1 Processing Time and Complexity 23
2.4.2 BER performance 26
2.4.3 Security Performance . 31
2.4.4 Indistinguishability 34
2.4.5 Latency 37
2.5 Summary 40
3 Integrated Satellite Network Security 42
3.1 Introduction . 42
3.2 Modeling 48
3.2.1 Eavesdropping Risk 49
3.2.2 Security Signal Structure 52
3.2.3 Onboard Power Modeling and Gaussian Beamforming . 54
3.3 Integrated Encryption and Gaussian Beamforming Framework 56
3.3.1 Formulation 56
3.3.2 Orthogonal Multiple Access 57
3.3.3 Non-Orthogonal Multiple Access 59
3.4 Integrated Cryptography and Physical Layer Security Framework . 63
3.4.1 Formulation 63
3.4.2 Onboard Power Allocation for Signal Transmissions and Security Computations 66
3.4.3 Joint Beam Scheduling and Signal Assignment 69
3.4.4 Security Algorithm Selection 72
3.5 Performance Evaluation 72
3.5.1 Secure Transmission Capacity 72
3.5.2 Computational Complexity . 76
3.6 Simulation Result . 77
3.7 Summary 80
4 Dynamic Downlink Transmission and ISL Handover Control 82
4.1 Introduction . 82
4.2 System Model and Problem Formulation 85
4.3 Dynamic Transmission and Handover Control 90
4.3.1 Lyapunov Optimization 90
4.3.2 Auxiliary Variable 93
4.3.3 Admission Control 93
4.3.4 Joint Scheduling and Power Allocation 94
4.4 Simulation Result . 97
4.5 Summary 100
5 Conclusion 102
6 Appendix 104
6.1 Probability Density Function (PDF) of the Product of the Squared Nakagami-m Fading and Gaussian Beam Pattern in Section 3.2.1 104
6.1.1 PDF . 104
6.1.2 Mean and Variance 105
6.2 Channel Capacity of the Encryption Signal in 3.3.1 106
6.3 Upper Bound of the DMU in 4.3.1 . 108
References 110DoctordCollectio